Event Sourcing & CQRS — Simple

flowchart LR
  C([Command])
  WM[Write model<br/>commands -> events]
  ES[(Event store)]
  P[Projector]
  RM[(Read model)]
  Q([Query])
  C --> WM --> ES
  ES --> P --> RM
  Q --> RM

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class C,WM,P,Q service;
    class ES,RM datastore;

Event sourcing: state = sequential log of immutable events; the current state is a projection (replay). CQRS: separate write model (commands → events) from read model (queries over projections).